A Source For The Graph, Ctd

Looks like it was made by Tehran Bureau, which has lots of other election coverage. Their analysis:

Statistically and mathematically, it is impossible to maintain such perfect linear relations between the votes of any two candidates in any election and at all stages of vote counting. This is particularly true about Iran, a large country with a variety of ethnic groups who usually vote for a candidate who is ethnically one of their own. For example, in the present elections, Mr. Mousavi is an Azeri and speaks Turkish. The Azeries make up 1/4 of all the eligible voters in Iran and in his trips to Azerbaijan province, where most of the Azeri population lives, Mr. Mousavi had been greeted by huge rallies in support of his campaign. Likewise, Mr. Karroubi, the other reformist candidate, is a Lor. But according to the data released by Iran’s Interior Ministry, in both cases, Mr. Ahmadinejad has far outdone both candidates in their own provinces of birth and among their own ethnic populations.